1. Field of the Invention
The system and method of the present invention relates to three dimensional computer graphic modeling, and more particularly to setting and visualizing parameters of a virtual camera in a three dimensional graphic model to control later photorealistic rendering by a computer.
2. Background
The use of computers to generate photorealistic three dimensional images has become widespread. Computers frequently are used to generate and/or display three-dimensional images, pictures and moving images such as video and movies. Animation using the computer is quite common. These images are generated a variety of ways. For instance, an image may be computer generated through software executing on the computer. At other times real world images are imported from another media, such as film or a camera and lens apparatus electrically connected to the computer system. Computers also are being used to combine real world images and computer generated images.
Production of photorealistic images from three dimensional computer graphic models may be very time consuming, possibly taking several hours to produce a single image. The production of photorealistic images may be split into a modeling phase and a rendering phase. Artists may build and manipulate the graphic models in the modeling phase which may be optimized for real-time interaction. The modeling phase may produce a description of the scene that is passed to the rendering phase where the photorealistic images are produced without artist involvement.
The production of even a single photorealistic image may not be feasible in real-time. In particular, the generation of photorealistic moving images in real-time is extremely difficult. Artists preparing photorealistic three dimensional images often work with simplified representations of the scenes they are preparing. For example, an artist may work with wireframe models in which objects are represented by meshes of lines that only suggest the size and shape of an object. In other cases, previsualizations may be generated that show the appearance of objects but simplifying or omitting most of the subtle photographic effects to reduce the time and/or computing power required to generate the previsualization images. The fully rendered image is generated only after the scene has been completed based on the use of the simplified presentations of the computer model. Since the rendering of the final photorealistic three dimensional images may be time consuming and costly, it is desirable that the artists preparing the scene achieve the desired result before the final image is rendered.
A digitally simulated virtual camera may be part of the computer graphic model to control the rendering of the three dimensional model as a two dimensional photorealistic image. The rendering of a computer generated image may be controlled by the virtual camera. The virtual camera provides parameters such as position, orientation, and lens settings equivalent to the parameters of a physical camera and lens system. The rendering software may use some or all of the camera parameters to achieve photorealism of the final rendered images. For example, the rendering software may use the focus setting of the virtual camera's lens to determine what objects will be rendered in sharp focus and which will appear blurred to suggest being out of focus. The artist may adjust the parameters of the virtual camera—such as focus, focal length, and aperture—to achieve the desired photographic effect. It will be appreciated that all apparent optical effects of the virtual camera are entirely the result of computation performed by the rendering software and there are no real optical effects involved in the rendering process.
Modern photographic camera equipment and lenses contain a number of fixed and adjustable elements or parameters that may be modeled by the rendering software and affect the appearance of the final rendered images. The film gate (sometimes referred to as the aperture) represents a horizontal and vertical dimension of the image being exposed onto the photographic film or, in the case of the video camera, the size of the video image recording chip. The f-stop (sometimes also referred to as the aperture) on the lens controls the amount of light striking the film gate. The focal length of the lens identifies the distance from the rear nodal point of the lens to the surface of the focal plane. The focus represents a distance in front of the camera. The field of view is the area photographed by the lens and contains the images captured through the lens. The circle of confusion provides a measure of image clarity or sharpness of focus for a point. A camera typically has a focus ring to control focus from a setting of infinity to distances typically in the range of two to three feet. On a zoom lens a second control exists to manipulate the focal length.
The settings of these different features may be expressed using different scales and units. For example, the focal length typically is expressed in millimeters. The film gate (aperture) typically is expressed in thousandths of an inch. The actual film stock in the aperture typically is referred to in millimeters. The f-stop is a logarithmic scale based on light transmission through the lens. The focus is typically set in feet, or sometimes in inches or meters. The field of view is typically expressed as an angle of degrees either horizontal, vertical or diagonal. In addition, the relationship between the horizontal and vertical dimensions of the aperture, referred to as the aspect ratio, is represented as a single number assumed to be a ratio to a value of 1. Motion picture examples include 1.33:1, 1.66:1, 1.85:1, 2.20:1, 2.35:1. These typically are referred to as “1.33”, “1.66”, “1.85”, “2.20”, “2.35”; which represents how wide the format appears to be to the viewer in relation to the image height. In addition, the circle of confusion is typically measured in thousandths of an inch.
A typical 3D software modeling package does not provide a preview of the effects of virtual camera lens adjustments. Some 3D software modeling packages, such as those marketed by SOFTIMAGE, an Avid Corporation, Inc. company, provide control of the lens characteristics such as f-stop, focus, and the circle of confusion. However, the lens characteristics provided are used strictly for the creation of the photorealistic computer graphic image as the final step in the simulation process.
When objects are defined within a computer graphics software environment, a camera object is usually specified solely in order to provide a particular view of those objects. Since the system is an electronic simulation and does not use light rays or an optical system to capture and record the image, physical real world issues like focus do not come into play. Instead the images are viewed by the user on the computer system or recorded out to a picture file. For example, all objects in a preview computer graphics image may be shown as though all objects were in perfect focus.
For these reasons, computer graphics images are normally sharp during the interactive phase when the images are generated and combined with other images, as the images presented to the user during that phase do not take lens characteristics into account. Typically an attempt to simulate the effects of focus and other lens artifacts are applied as part of a separate and last rendering step in the creation of a final computer graphic image, i.e., subsequent to the interactive phase controlled by the artist.
The computer modeling environment used by the artist may not provide adequate feedback of lens values, or determinations of exact boundaries or locations of lens effects. Furthermore, the calculations typically used to derive the final field of view for a particular lens in a 3D modeling package contains assumptions, omissions, oversights and oversimplifications of the real world equivalent true lens and camera combinations. Most notable are the lack of solving for the effects of change in focus as it relates to focal length and the lack of equivalent controls compared to a real world camera. The relationship among lens attributes, such as focal length, focus and f-stop are not well understood or implemented in current software packages and do not successfully address the problems and details of simulating the changes in these optical characteristics. To appreciate this, consider that a nominal 100 mm lens focused at 2 ft. has a true focal length of nearly 120 mm.
Effects, such as the changing of focal length as a lens is focused, are obscured to the observer by the pronounced effects of blurring as the object goes in and out of focus. In the situation where matching a real world environment to a computer-generated object is not exact, the situation is oftentimes only fixed through trial and error and a user may need to guess tolerances and measurements as an approximation to regenerate a combined image multiple times to see what “looks best.”
In addition, currently available 3D software modeling packages do not contain some of the features common to many real world cameras, such as interchangeable reference clips and direct and interactive control of focus, zoom values and depth of field. These missing elements constitute important technical considerations for getting the exact lens setting as close as possible to the settings of the real world camera and for being able to operate a computer graphics virtual 3D camera in the same manner and ease as a real world camera.
The virtual camera and lens system and method of the present invention addresses the setting and visualization of the settings, prior to rendering, of a computer graphic, virtual, three dimensional camera and lens model having the variables and features of a real world camera and lens device.